1. Field of the Invention
The present invention relates to a diagonal image adjusting device in a plate cylinder, more specifically, to a diagonal image adjusting device which carries out diagonal image adjustment by shifting a clamping part in a direction of a shaft of the plate cylinder.
2. Description of the Prior Art
As shown in FIG. 8, a plate 10 is rolled on a plate cylinder 60 which is used for offset printing. Offset printing is carried out by supplying both ink and dampening solution to the plate 10 which rotates together with the plate cylinder 60 rotating about a plate cylinder shaft 60J. A cut-out part 61 is formed in the plate cylinder 60, and both a leading edge side clamping base 62 and a tail edge side clamping base 63 are provided in the cut-out part 61.
A leading edge side clamp 64 is located on the leading edge side clamping base 62. A leading edge side part 10a of the plate 10 is clamped between the leading edge side clamping base 62 and the leading edge side clamp 64. In the same manner, a tail edge side clamp 65 is located on the tail edge side clamping base 63. A tail edge side part 10b of the plate 10 is clamped between the tail edge side clamping base 63 and the tail edge side clamp 65.
In a typical procedure, in order for the plate 10 to fit onto a surface of the plate cylinder 60 by applying tension, both the tail edge side clamping base 63 and the tail edge side clamp 65 are moved in a direction shown by arrow 90.
In multi-color printing, a plurality of colors are printed so as to overlay one another on a printing paper. It is, therefore, necessary to carry out an accurate register adjustment of the plate 10 to the plate cylinder 60 to achieve high quality printing as a result of preventing displacement in colors.
Diagonal image adjustment of the plate 10 on the surface of the plate cylinder 60 is difficult to carry out when the plate 10 is rolled on the plate cylinder 60 with diagonal displacement. Such diagonal displacement may be frequently observed when the leading edge side part 10a of a plate 10 having a short length is clamped by the leading edge side of a clamping apparatus and rolled on the plate cylinder 60.
Japanese Patent Laid-open Publication No. 193351 of 1997 (Hei 9-193351) discloses a clamping apparatus for a plate which is used for adjusting diagonal displacement of the plate 10 disposed on the plate cylinder 60. The prior art structure of the clamping apparatus will be described with reference to FIG. 9 and FIG. 10. FIG. 9 is a plan view of the plate cylinder 60, and FIG. 10 is a cross sectional view looking in the direction of arrow V of FIG. 9.
The leading edge side part 10a of the plate 10 is clamped between the leading edge side clamping base 62 and the leading edge side clamp 64, and the tail edge side part 10b of the plate 10 is clamped between the tail edge side clamping base 63 and the tail edge side clamp 65 (see FIG. 8).
Thereafter, both the tail edge side clamping base 63 and the tail edge side clamp 65 are moved in directions shown by arrow 92 or by arrow 93 with clamping of the tail edge side part 10b therebetween. Diagonal image adjustment of plate 10 can be carried out by the movement in the directions as a result of correcting the diagonal displacement of the plate 10 to the cylinder 60 on the surface thereof. The structure of the prior art clamping apparatus will be described hereunder.
A groove 28 extended in the directions shown by the arrows 92, 93 is formed at an end of the tail edge side clamping base 63 as shown in FIG. 9 and FIG. 10. A block 29 is inserted into the groove 28. The block 29 is slidably movable along with the groove 28 in the direction shown by the arrows 92, 93 relative to the tail edge side clamping base 63.
The block 29 is supported so as not to be moved in the directions shown by the arrows 92, 93 relative to the cylinder plate 60. An adjustment bolt 30 is screw threaded into the tail edge side clamping base 63 through a sidewall thereof. The block 29 is screw threaded and is passed through by the adjustment bolt 30.
A cut-out 30S for operation is formed in a side part of the tail edge side clamping base 63, and the end 30H of the bolt 30 protrudes in the cut-out 30S. The adjustment screw 30 can be tightened and loosened by rotating the screw 30 with a tool such as a spanner connected thereto through the cut-out 30S when the diagonal image adjustment is carried out.
A coil spring 31 is disposed around the screw 30, and the spring 31 is located between the block 29 and a side wall 36. The spring 31 prevents occurrence of backlash of the threads of the bolt 30 as well as pushing a collar 32 of the bolt into contact with the tail edge side clamping base 63.
In order to carry out diagonal image adjustment, the screw 30 is rotated with a spanner and the like. As described above, the block 29 is screw threaded and is passed through by the bolt 30, and the block 29 is supported so as not to be moved in the directions shown by the arrows 92, 93 relative to the cylinder plate 60. Consequently, the bolt 30 is moved in the directions shown by the arrows 92, 93 relative to the block 29 when the bolt 30 is tightened and loosened.
The tail edge side clamping base 63 is moved in the directions shown by the arrows 92, 93 according to the movement of the bolt 30. The diagonal image adjustment of the plate 10 is carried out as a result of moving the tail edge side clamping base 63 in the directions. The leading edge side clamping base 62 can be moved swingably around a pin 62P shown in FIG. 9. In this way, deflection of the plate 10 caused by the diagonal displacement thereof to the cylinder 60 on the surface thereof is corrected.
However, the structure of the prior art clamping apparatus have the following problems to be resolved. It takes much time and work to carry out the diagonal image adjustment because a tool such as a spanner is used to rotate the bolt 30.
Further, the use of a tool such as the spanner and the like is undesirably required to operate the bolt 30, so that the operation must be carried out indirectly. In this connection, the diagonal image adjustment can not be carried out accurately because the subtle adjustment is difficult to carry out for the indirect operation compared to direct operation by hand.
In addition, such subtle diagonal image adjustment can not be carried out with a desired accuracy since the diameter of the end 30H of the bolt 30 is relatively small. Although, occurrence of backlash of the threads of the bolt 30 is prevented by the spring 31 as described above, the tail edge side clamping base 63 tends to move a distance more than a desired range according to the rotation of the end 30H of the bolt 30 because of the diameter thereof. As a result, the diagonal image adjustment can not be carried out with the desired accuracy.
The use of another end 30H of the bolt 30 having a larger diameter might interfere with the printing work because the end 30H protrudes from an outer plane 60F (see FIG. 10) of the plate cylinder 60. In other words, the tail edge side clamping base 63 is located adjacent to the surface in order to clamp the tail edge side part 10b of the plate 10 between the tail edge side clamping base 63 and the tail edge side clamp 65, and the bolt 30 is provided to the tail edge side clamping base 63. Therefore, another end 30H of the bolt 30 having a larger diameter undesirably protrudes from the outer plane 60F (see FIG. 10) of the plate cylinder 60.
Further, the cut-out 30S for operation is formed at the side part of the tail edge side clamping base 63 for rotating the bolt 30. The strength of the plate cylinder adjacent to the cut-out 30S (side part) is undesirably decreased. A large sized cut-out 30S needs to be formed responding to the diameter of the end 30H of the bolt 30 when the end 30H having a larger diameter is used. As a result of forming the large sized cut-out 30S, the strength of the plate cylinder adjacent to the cut-out 30S is further decreased.
Alternatively, the strength of the plate cylinder in the side part can be maintained in a certain range when a side wall of the plate cylinder 60 is located outside of the end 30H without forming the cut-out 30S in the side wall of the tail edge side clamping base 63. The overall length of the plate cylinder 60 becomes longer than that of the original plate cylinder, so that the printing machine utilizing the plate cylinder comes to a large-scale printing machine.